Contributors CMO'L was the primary contributor to the paper in relation to the concept and design, analysis and interpretation of data,
and drafting of the article. JJK designed and ran the original cohort study from which these data arose. NN, CB and EG supervised
CMO'L in the analysis of data. SRZ provided expertise in the area of psychology and the imputation analyses. All authors contributed
to the interpretation of data and reviewing of the article, and provided final approval for the version to be published.

Accepted 7 September 2009

Published Online First 19 October 2009

Abstract

Background When examining the association between prenatal alcohol exposure and fetal effects, the timing and intensity of exposure
have been ignored in epidemiological studies. The effect of using dose, pattern and timing of consumption (“composite” method)
was investigated in this study, to examine the association between prenatal alcohol exposure and fetal effects.

Methods The composite method resulted in six categories of exposure (abstinent, low, moderate, binge <weekly, binge 1–2×/week and
heavy). The odds of language delay and child behaviour problems were calculated for the composite method and then compared
with an analysis using averaged estimates of <1 and 1+ drinks per day and with stratification by quantity ignoring dose per
occasion. Data used for the analyses were from a 10% random sample of non-Indigenous women delivering a live infant in Western
Australia (1995–1997). Participants from the 1995-1996 cohort were invited to participate in an 8-year longitudinal survey
(78% response rate n=2224; 85% were followed-up at 2 years, 73% at 5 years and 61% at 8 years).

Results The effect of moderate and binge levels of exposure was only evident with the composite method; anxiety/depression following
first-trimester moderate exposure (OR 2.24, 95% CI 1.16 to 4.34), and following late pregnancy moderate (aggressive behaviour
OR 1.93, 95% CI 0.91 to 4.09) and binge (language delay OR 3.00, 95% CI 0.90 to 9.93) exposures. Results for heavy levels
of exposure were similar with each method. The estimates for late pregnancy were imprecise due to small numbers.

Footnotes

Funding The Western Australian survey of health-related behaviours and events during pregnancy and early infancy was funded by grants
from Healthway (the Western Australian Health Promotion Foundation (94/2705, 96/49078 and 98/8016)).

Competing interests None.

Ethics approval Ethics approval for the conduct of this study was granted by the Princess Margaret Hospital Research Ethics Committee and
the WA Confidentiality of Health Information Committee.